1. Field of the Invention
The present invention relates to an image processing apparatus and to a method for controlling this apparatus.
2. Description of the Related Art
There are conventional image processing apparatus with which the contour (edge) of an image is detected and contour enhancement processing is performed according to the characteristics of the contour. Also known is an image processing apparatus with which the type of subject in an image is determined, and image processing is performed according to the determined type of subject.
For example, Japanese Patent Laid-Open No. 2000-59651 discloses an image processing apparatus with which the degree of contour enhancement is controlled according to the brightness level of an input signal. With the technique of Japanese Patent Laid-Open No. 2000-59651, the contour enhancement is weakened for video signal portions with a low brightness level, and is strengthened for video signal portions with a high brightness level. Also, Japanese Patent Laid-Open No. 2002-190984 discloses an image processing apparatus which determines whether an image is a landscape image or a text image, and if it is a text image, performs control to strengthen the contour enhancement.
With the technique disclosed in Japanese Patent Laid-Open No. 2000-59651, however, because the degree of contour enhancement is controlled on the basis of just the brightness of the contour to be corrected, contour enhancement will be performed to the same degree as long as the brightness is the same, no matter what the contour portion of a subject is. As a result, depending on the subject, the contour enhancement may be too strong, or conversely it may be insufficient, which is a problem in that the proper processing cannot be performed adequately on the subject.
With the technique disclosed in Japanese Patent Laid-Open No. 2002-190984, the type of image (whether it is a text image or a landscape image) is determined according to the brightness distribution. However, Japanese Patent Laid-Open No. 2002-190984 does not disclose a discrimination technique that is suited to discriminating between anything other than a text image and a landscape image (such as discriminating between a manmade object such as a building and a natural object such as a flower or a landscape). Even if an attempt was made to utilize the technique of Japanese Patent Laid-Open No. 2002-190984 to discriminate between manmade and natural objects, it would still be difficult to discriminate with high accuracy because no clear characteristic difference is obtained in relation to the brightness distribution between manmade and natural objects. Therefore, it is difficult to change the degree of contour enhancement between buildings and natural objects, for example.